After a two-month pause, Microsoft's newest and oldest operating systems return to trend form

Windows 8 surged in December to end the year with almost 12 percent of the user share of all Windows personal computers, while the destined-for-retirement Windows XP restarted its decline after a two-month pause, a Web analytics company said Thursday.

Both were good signs for Microsoft, which has bet its future on Windows 8 and implored customers to abandon the aged Windows XP.

According to Net Applications, Windows XP fell 2.2 percentage points in December to 29 percent of all desktop and notebook computers worldwide, the first time it breached that 30-percent barrier. But the 12-year-old operating system still accounted for nearly a third -- 32 percent -- of Windows-powered PCs.

Both operating systems had taken a break in October and November from earlier trends: Windows XP's gradual decline and Windows 8's deliberate growth.

Their December changes were the largest since September, Net Applications data showed.

The gain by Windows 8 and 8.1 was likely due to new PC purchases in the last month of 2013: Most consumer systems come equipped with the newest version, Windows 8.1, which accounted for 34 percent of the combined total, up from November's 28 percent.

Windows 8's increase put some more distance between it and Windows Vista, the 2007 OS bust: The gap between it and Windows 8 increased by seven-tenths of a percentage point in December.

But Windows 8 remained far behind Windows 7's adoption. Fourteen months after its debut, Windows 7 powered 23.1 percent of all Windows systems, nearly twice that of Windows 8. In fact, Windows 7 grew its user share last month, adding nine-tenths of a percentage point to end December at 47.5 percent of all computer operating systems, and at 52.4 percent of those running a flavor of Windows. Both were records for the 2009 operating system, hinting that it will remain a standard for years to come.

The decline in Windows XP may have contributed to the increase of Windows 7 as well as Windows 8 and 8.1, as some users migrated from the 2001 OS to Windows 7 as a way to forestall trying the radically-redesigned Windows 8. Most businesses, analysts have said, will stick with Windows 7 as long as possible rather than incur the costs of another migration.

Microsoft must be smiling at the revival of Windows XP's downturn: The company has been aggressive in its efforts to convince customers to ditch Windows XP before it's retired from security support on April 8, 2014. For the most part, those messages have been received, even if Microsoft would prefer a faster rate of desertion: In the last 12 months, XP's user share has dropped 10 percentage points, representing a 26 percent decline.

Using XP's average changes over the last 12 months, Computerworld now forecasts that Windows XP will power between 25 percent and 26 percent of all personal computers at the end of April.

Net Applications measures operating system user share by tracking unique visitors to approximately 40,000 sites that rely on its analytics software.

The California company's figures are usually at odds with what rival StatCounter generates because the two measure usage differently. While Net Applications tracks user share -- how many unique users run a specific operating system -- StatCounter tallies usage share via page views to show how active users of each OS are on the Internet.